Since long ago, various kind of sterilization means have been applied to articles of every species such as disposable or recyclable medical apparatuses and food containers, and there have also been proposed indicators for conveniently distinguishing whether such a sterilization treatment has been made or not. For example, Japanese Patent Application Laid-Open (Kokai) No. 36172/1984 discloses an indicator for gas sterilization treatment with use of ethylene oxide; and Japanese Patent Application Laid-Open (Kokai) Nos. 287972/1986, 43827/1993 and 65441/1993 each disclose an indicator ink for electron beam sterilization. The latter group of Laid-Open (Kokai) Applications each mention an indicator wherein a pH indicator is used in combination with such a high molecular compound as is capable of generating hydrogen chloride when irradiated with electron beam.
On the other hand, as a means to conduct a sterilization treatment without adversely affecting medical equipments which are produced from various materials, there have recently been proposed and put into practice a hydrogen peroxide plasma sterilization method and an apparatus therefor (See: Japanese Patent Publication (Kokoku) Nos. 62261/1990 and 22693/1995). This sterilization method summarily comprises a step of contacting an article to be sterilized, with hydrogen peroxide vapor under reduced pressure in an air-tight chamber, and then generating hydrogen peroxide plasma. This method can be said to be a very useful one, not only in that high sterilization efficiency is attained but also in that, when plasma state is ended, hydrogen peroxide is converted into water and oxygen which are quite harmless.
The above-mentioned Japanese Patent Publication (Kokoku) No. 22693/1995 discloses a liquid-dispensing cassette to be used in a plasma sterilization apparatus which cassette is equipped with a cell for containing a hydrogen peroxide solution. It is further disclosed that said dispensing cassette may be equipped with an indicator strip having a color tone with which to detect the leakage of hydrogen peroxide solution from the liquid-containing cell. Said Publication does not concretely disclose, however, how to constitute the indicator strip.
Also in putting a hydrogen peroxide plasma sterilization method into practice, it would be desirable that there should be available such an indicator which can easily distinguish whether or not a sterilization treatment has been given to an article to be sterilized, as is employed in the aforementioned gas sterilization treatment with use of ethylene oxide or electron beam sterilization treatment. Thus, the object of this invention is to provide both a sheet having a chemical indicator composition layer (or an indicator function layer) which can distinguish whether or not a hydrogen peroxide plasma sterilization treatment has been given to an article to be sterilized, and a packaging bag for plasma sterilization having said composition layer.